Functional Description
1505
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
1-Wire Master Module
the slave does not know it is supposed to reply, the line remains untouched and is read as a 1 (and
written as a 1).
•
Usually at the end of one or more commands to that slave, a reset is issued again.
The 1-Wire module supports reset and answer-to-reset on request (although answer-to-reset can be
suppressed). It also supports byte operations. The software chooses which read, write, or mixed operation
to use. Partial byte (bit or multi-bit) is also supported.
22.3.3 Overdrive
The 1-Wire Module allows for an overdrive speed to be selected for shorter line lengths. Overdrive is
about ten times faster because it uses smaller time periods. It is agreed by both master and slave before
enabling. Overdrive is selected using the ODRV bit of the 1-Wire Control and Status (ONEWIRECS)
register.
In overdrive mode, the time periods shrink.
shows the active time for 1-Wire operations in
overdrive mode. For example, the Master typically drives and holds the line low for 15 µs for a write 1, but
in overdrive mode this is 1 µs.
Table 22-1. Active Time Periods in Overdrive Mode
Operation
Time
Notes
Write 1
1 µs low
Less than 2 µs low
Write 0
7.5 µs low
Up to 10 µs low
Read 1
1 µs low
Master samples at 2 µs
Read 0
9 µs low
Slave holds at least 7 µs
Reset
70 µs low
Note 2 µs delay before reset for safety
Answer to Reset
4 µs to 48 µs
Master samples at 8.5 µs
22.3.4 Timing Override
The 1-Wire module can manually override timing for any main action. Each non-zero value in the 1-Wire
Timing Override (ONEWIRETIM) register replaces the default normal or overdrive time rule.
The time factors that can be controlled:
(1)
If W0TIM has been programmed to a non-default value, W0REST must be programmed for correct functionality.
Table 22-2. Bit Field Definitions for 1-Wire Timing and Override (ONEWIRETIM) Register
Name
Meaning
Range (if
used)
Scale
Default
(normal)
Default
(overdrive)
W1TIM
Amount of time to drive and hold line low for a write 1
1 to 15 µs
1 µs units
6 µs
1 µs
W0TIM
Amount of time to drive and hold line low for write 0
(1)
4 to 124 µs
4 µs units
60 µs
7.5 µs
W0REST
Amount of time to hold line high after a write 0 (rest)
1 to 15 µs
1 µs units
10 µs
2.5 µs
W1SAM
Amount of time after 1-Wire has released the line to
sample slave holding line
1 to 15 µs
1 µs units
10 µs
1 µs
RSTTIM
Amount of time to drive and hold line low for a reset.
Allow for an additional 2-µs prereset period
32 to 2016
µs
32 µs units
480 µs
70 µs
ATRTIM
Period of answer-to-reset or rest. The ATRSAM bit value
must be considered when programming this field.
ATRTIM must be greater than ATRSAM to avoid a
STUCK fault generation
16 to 496 µs
16 µs units
240 µs
48 µs
ATRSAM
Period in which first sample occurs in answer-to-reset
(after line goes high). If the SKATR bit is set in the
ONEWIRECS register, this value indicates the rest
period after reset
8 to 120 µs
8 µs units
10 µs
2 µs